My fetish started when I was around eighteen and I've been enjoying it ever since. My mother's friend would pop on and see us nearly every day she was quite slim but had a really big round bum. I could never take my eyes off it she always wore really tight trousers or tracksuit bottoms , both really clung to her shapely ass. I'm sure she caught me looking at her ass but if she minded she never said anything , I'm sure she knew I liked it because she stuck it out in front of me at every opportunity. Anyway as time went on I really wanted to feel her big round bum and I took every opportunity to squeeze past her when I could. Sometimes she'd have her back to me and as I'd go past I'd just let my hand brush past her bum . Having a sneaky feel of her ass turned me on so much I had to wank myself off as soon as I got to my room. One day she parked her car on our drive and was complaining that something was knocking underneath and could I help her find it. Of course I said yes there wasn't a lot of room on are drive so I was getting excited that another brush past on her big bum was probably going to happen. I finished off what I was doing and I got a much bigger treat than I was expecting. She was bent over on all fours with half of her body under the car and her big bum sticking right out. Her tracksuit bottoms were drum tight ready to split any second. My first thought was to give it a smack it looked so inviting but I thought better of it , but I did rest my hand fully on her bum as I got down beside her to help. I said sorry for putting my hand there but I said I wanted to steady myself because there wasn't much room. That's okay was her reply I dont mind . I wished then that I left my hand on her ass a bit longer. My cock was already hard all I could think about was getting to my room for a wank . But the best was still to come , I had to make my way to the other side of her to get a better view of what was causing the problem. I stayed on all fours and started to make my way past her. It wasnt long before my head was dead level with her massive big round ass. I was in heaven , I knew not to touch again, although I honestly dont think she would have minded, so I put my nose up close to her bum and pussy and had a really long sniff. The sweet musty aroma was intoxicating I stayed there sniffing for as long as I dared it was so exciting. We never found what the problem was but after that experience as a young lad it kept me wanking for weeks after. No need for me to say I've kept that fetish going to this day.